1. Technical Field
The invention relates to a cemented lens including at least two lenses cemented through cementing surfaces one of which is a concave surface of one of the lenses and the other of which is a convex surface of the other of the lenses, a method for manufacturing the cemented lens, and a projector apparatus using the cemented lens.
2. Description of the Related Art
As shown in FIGS. 8A and 8B, there has been known a cemented lens 50 composed of two lenses, that is, a first lens 51 and a second lens 52 cemented through cementing surfaces. One of the cementing surfaces is a concave surface 51a of the first lens 51. The other of the cementing surfaces is a convex surface 52a of the second lens 52. The cemented lens 50 configured thus is, for example, used as a lens for correcting chromatic aberration in an optical system of a projector apparatus etc. for projecting image light on a screen to thereby display an image. For example, the cemented lens 50 is produced as follows (for example, see JP Hei. 7-41339) . That is, transparent adhesive 53 is applied uniformly substantially all over the concave surface 51a of the first lens 51. The concave surface 51a and the convex surface 52a of the second lens 52 are then put on top of each other and bonded with each other. Thus, the concave surface 51a and the convex surface 52a are cemented. In the cemented lens 50 produced thus, the adhesive 53 is inserted between the cementing surface of the first lens 51 and the cementing surface of the second lens 52. As a result, the adhesive 53 is put into an effective area including the optical axis positions of the lenses 51 and 52 and serving as a chief optical path of the cemented lens 50.
However, there is a problem that the cemented lens 50 of the related art cannot be used in a place exposed to intensive light, for example, in a place close to an exit pupil of a projection lens for the project or apparatus. When the adhesive 53 is exposed to intensive light, the adhesive 53 is apt to be deformed to thereby cause discoloring of light. When the adhesive 53 is located in the effective area as in the cemented lens 50, transmitted light may be discolored and attenuated due to the deformation of the adhesive 53. When the cemented lens 50 is disposed near the exit pupil, the lens diameter of the cemented lens 50 becomes small. Therefore, the energy of light per unit area becomes so high that there arises a problem particularly. Thus, it is difficult to use the cemented lens 50 in a site exposed to intensive light, and the degree of freedom in designing the optical system is restricted.